To minimize air pollution from power plants and to reduce dependence on fossil fuels, some power plants that are considered to provide “renewable” energy have enjoyed increased popularity in recent years. Renewable energy is a category of power generation sources that primarily includes solar power, wind power, geothermal power and biomass power (including various different non-fossil solid fuels as a starter material). While mature non-fossil and non-polluting technology such as nuclear power and hydroelectric power generally avoid combustion of and depletion of fossil fuels in their use, these mature technologies are generally not considered to be in this “renewable” power generation category.
Renewable energy is often incentivized by various government and electric utility sponsored programs to make renewable energy more economically viable and to increase the utilization of such technology to provide electric power to the “grid” for consumption. Hence, it is generally desirable for those in the power generation market to deploy as much renewable electric power as possible.
Some of these renewable energy technologies still utilize a thermal cycle (typically a Rankine cycle) for power generation. In such a thermal cycle, it is necessary to pump a working fluid to an elevated pressure and then heat that working fluid to cause the working fluid to boil. This working fluid (typically water/steam) can be kept at a boiling point, in which case it is referred to as “saturated” steam or can also be referred to as “wet” steam. If additional heat is added to elevate the temperature above the boiling point, the steam is referred to as “superheated steam.” The working fluid is then routed through an expander, typically a steam turbine.
Steam turbines exhibit greatest efficiency generating power from higher temperature working fluids. State of the art steam turbines can handle an inlet temperature for the elevated pressure steam or other working fluid of at least 800° F., and typically as high as 1050-1200° F. Some experimental steam turbines have even operated at higher temperatures.
Renewable energy systems that utilize a heated working fluid typically include geothermal power plants, biomass power plants and solar thermal power plants. Solar thermal power plants are different from photovoltaic power plants in that the solar radiation is not used directly to generate electricity, but rather is utilized indirectly to heat water or some other working fluid. This heated water or other working fluid is then caused to boil and be expanded through a turbine to generate power.
Often such solar thermal power plants, geothermal power plants and biomass power plants each suffer from a common problem of not having sufficient heat available to raise the temperature of the working fluid (typically water) to a superheated temperature, and most preferably a temperature near a maximum inlet temperature that can be handled by the steam turbine. As a result, such renewable power generation systems exhibit significantly less efficiency than could otherwise be attained. This deficiency means that less power is generated from such renewable sources than the amount of power theoretically available from the renewable source.
Accordingly, a need exists for power generation processes which can take the wet steam, saturated steam or only slightly superheated steam from a source, such as a heated working fluid based renewable power plant and to raise the temperature of the working fluid up to an optimal temperature matching a maximum inlet temperature for the steam turbine. With such a system, higher efficiency and hence more power can be produced by the power plant. Such a steam reheater would benefit from having little or no atmospheric emissions of pollutants and possibly using renewable fuels.